Howard, Mark and Vala, Jiri (2012) Qudit versions of the qubit "pi-over-eight" gate. Physical Review A, 86 (022316). pp. 1-10. ISSN 1050-2947

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Abstract

When visualized as an operation on the Bloch sphere, the qubit "pi-over-eight" gate corresponds to one-eighth of a complete rotation about the vertical axis. This simple gate often plays an important role in quantum information theory, typically in situations for which Pauli and Clifford gates are insufficient. Most notably, if it supplements the set of Clifford gates, then universal quantum computation can be achieved. The "pi-over-eight" gate is the simplest example of an operation from the third level of the Clifford hierarchy (i.e., it maps Pauli operations to Clifford operations under conjugation). Here we derive explicit expressions for all qudit (d-level, where d is prime) versions of this gate and analyze the resulting group structure that is generated by these diagonal gates. This group structure differs depending on whether the dimensionality of the qudit is two, three, or greater than three. We then discuss the geometrical relationship of these gates (and associated states) with respect to Clifford gates and stabilizer states. We present evidence that these gates are maximally robust to depolarizing and phase-damping noise, in complete analogy with the qubit case. Motivated by this and other similarities, we conjecture that these gates could be useful for the task of qudit magic-state distillation and, by extension, fault-tolerant quantum computing. Very recently, independent work by Campbell et al. confirmed the correctness of this intuition, and we build upon their work to characterize noise regimes for which noisy implementations of these gates can (or provably cannot) supplement Clifford gates to enable universal quantum computation

Item Type:	Article
Additional Information:	This article is available at DOI: 10.1103/PhysRevA.86.022316 . We thank E. Campbell for helpful comments on a previous version of this paper. M.H. was financially supported by the Irish Research Council (IRC) as part of the Empower Fellowship program. J.V. acknowledges support from Science Foundation Ireland under the Principal Investigator Award No. 10/IN.1/I3013.
Keywords:	Qudit versions; qubit; "pi-over-eight" gate; Bloch sphere; quantum information theory;
Academic Unit:	Faculty of Science and Engineering > Mathematical Physics
Item ID:	4495
Depositing User:	Dr. Jiri Vala
Date Deposited:	16 Sep 2013 15:43
Journal or Publication Title:	Physical Review A
Publisher:	American Physical Society
Refereed:	No
URI:	http://pra.aps.org/
Use Licence:	This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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